From NPR News, this is ALL THINGS CONSIDERED. I'm Melissa Block. For decades, kale was out of favor, often relegated to garnish status. But this dark, leafy, kind of chewy green is making a comeback. People who study such things say kale is now on 400 percent more restaurant menus than it was just four years ago.

And like an indie band that's hit it big, kale has a core group of fiercely devoted fans who suddenly find themselves among new converts. NPR's Dan Bobkoff went in search of a few early adopters to find out why, for them, kale is so much more than a vegetable.

DAN BOBKOFF, BYLINE: For kale people, talking about this cabbage relative is like talking about a lover.

BOBKOFF: I found Drew Ramsey in his natural habitat - the Union Square farmers' market in Manhattan.

RAMSEY: There's some kale right there. You don't even have to walk like, 5 feet.

BOBKOFF: Ramsey is a psychiatrist by day and kale fiend - well, all the time.

RAMSEY: Try a little leaf of the winterbor, and compare it to the rainbow lacinato.

BOBKOFF: Kale aficionados have been known to wear kale T-shirts and sport kale stickers. Ramsey is trying to launch a national kale day, and co-wrote a cookbook combining two cultural tropes.

RAMSEY: The book is "50 Shades of Kale."

BOBKOFF: Here's an excerpt.

RAMSEY: (Reading) Nothing is sexier than a sharp, happy mind atop a lean, healthy body. Few foods are able to deliver this promise like kale.

BOBKOFF: Kale people are everywhere, not just in hipster enclaves like Brooklyn. But if you happen to walk around there, it doesn't take long to meet someone like Aden Losher(ph).

ADEN LOSHER: Oh, I love kale. It's the best.

BOBKOFF: To meet this kale fatuation, Joe Orr set up a business, The Kale Factory. For $8 a box, you, too, can buy artisanal kale chips made by hand.

JOE ORR: She's taken the kale. She has a little bucket of sauce there, and she's taken each leaf, and very carefully and thoughtfully laying out that single leaf.

BOBKOFF: They come in flavors like Bombay ranch and vegan cheese, even cocoa. It's a sign this green is stepping into the mainstream.

MAEVE WEBSTER: Kale is definitely experiencing its moment right now.

BOBKOFF: Maeve Webster is senior director at Datassential, which tracks menu trends. Consider this: Earthbound Farm, which sells salad greens at supermarkets, says it's selling eight times the kale from two years ago. Kale is for sale at Wal-Mart. It's not tomato popular, but it's growing fast. And Webster says this is not just about health food stores and chichi restaurants.

WEBSTER: We see it at Starbucks - they have a few items with kale; Cheesecake Factory has added a salad that includes kale.

BOBKOFF: Kale's popularity has, shall we say, grown organically. Some celebrities swear by it, but there are no ads for kale. There's no kale lobby, but it does have this guy.

ROBERT MULLER-MOORE: Well, my name is Robert Muller-Moore, but everybody calls me Bo, the "eat more kale" guy.

BOBKOFF: Muller-Moore has been kale folk hero since he started selling hand-stenciled Eat More Kale T-shirts in 2001. That year, a Vermont farmer friend had a bumper crop and wanted a little marketing help. Back then, he says the shirts raised eyebrows.

MULLER-MOORE: They would look at me, my ponytail and my beard, and they would assume that kale was code for marijuana.

BOBKOFF: Thousands of shirts later, that doesn't happen so much these days, and it doesn't hurt that its wares caught the eye of fast food chain Chick fil-A, which thought "Eat More Kale" sounded too much like its slogan, "Eat More Chicken." It sued Muller-Moore, which sent his shirt sales through the roof, and even inspired Vermont state Sen. Anthony Pollina to try to make kale the state vegetable this year.

STATE SEN. ANTHONY POLLINA: Well, kale is very hearty, as we know. It's very resilient, just like Vermonters.

BOBKOFF: But yes, kale has some advantages over other greens - long-growing season, versatile; it packs more vitamins and minerals than just about anything you could eat. But there are other, similar healthy greens. I asked Muller-Moore why some people hitched their identity to kale and not, say, Swiss chard.

MULLER-MOORE: I think it's a club, and I think people are proud to be in the club.

BOBKOFF: So for kale people, saying you love kale is really a kind of shorthand, a way of saying "I'm in the know. I care about food and nutrition and farming." Loving kale is almost political.

MULLER-MOORE: I think that they're conscientious. I think that they give me a dern.

BOBKOFF: But now that kale is creeping into the mainstream, Drew Ramsey, the guy who wrote "50 Shades of Kale," worries about its cool factor.

RAMSEY: I fear kale backlash, if you want to be honest - right? Because there are a lot of other great leafy greens. We've seen some blog posts recently; people saying, you know, what about collards?

BOBKOFF: But at least for now, I haven't seen any Eat More Collards T-shirts.